Selective radioreceiver



March 22, 1932. H. F. ELLIOTT 1,850,831

SELECTIVE RADIORECEIVER I Filed April 21, 1928 2 sheets-sheet 1 4: Amp/fliers I; Da/sc/ars HIM-- LL] 0) z 3 1 8 3 32 m PIE. 2. 5 z I 33 [LI l o I Lu I 980 I010 FREQUENCY m KILOCYCLES INVENTOR HIS ATTORNEY March 1932- H. F. ELLIOTT SELECTIVE RADIORECBIVEH Filed April 21, 1928 2 Sheets-Sheet 2 BY v 1 ATTORNEY Patenged Mar. 22, 1932 UNITED STATES PAT OFFICE HAROLD F. ELLIOT'L'OI' PALOAL'I'O, CALIFORNIA, ASSIGHOB, BlIHFSNE ASSIGNMENTS, '10 RADIO CORPORATION 01' AMERICA, 01' NEW YORK, N. Y A CORPORATION 01'.

DELAWARE snmcrrvn namonncnrvna Application filed April 21,

ence.

Since there may be a large number of close- 1 1y spaced transmitting stations operating simultaneously, each carrying signals at different frequencles, it is important to make it possible to receive signals from one station to the exclusion of the others, by making the receiver discriminatory with respect to fremake it possible readilyto select the station'- quency. This has been accomplished by the provision oftunable circuits, which can be made resonant to the frequency at which reception is desired; but experience teaches that such resonant circuits, even if multiplied, can yet pass a sufficient volume of interferlng signals to produce disturbance, especlally 1f the interfering stations are powerful ornear by. i Y

It is one of the objects of my invention to from which reception is desired, to the substantial exclusion of the other stations that maybe simultaneously transmitting, and especially to accomplish this result by the aid of simple and inexpensive apparatus.

It is another object of my invention to pro vide aunit control systemthat' canoperate the various tunable circuits in unison.

The ideal condition for selectivity would I be one in which a narrow band of frequencies alone can pass to the receiver, for example, a band of about 10,000 cycles, which band can be moved atwill from one end of the range ofreception. to the'other. With the aid of my invention this idealcondition can be closely approximated- I In connection with the lsuperheterodyne system ofradio reception, my invention is particularly advantageous. In such superheterodyne systems, the carrier frequency that is received is combined with a frequency either above or below it to produce a beat frequency of intermediate value, but above the range of audibility. This beat frequency then carries the signals, which can be detected and amplified at the intermediate frequencies, and then later, again detected and passed to audio frequency amplifiers. It is placed a ter 1928. Serial No. 271,862.

evident, insuch a system, that the same beat frequency could be produced by another interfering station which is transmitting on a carrier wave displaced from the; frequency of the local oscillator by the same amount as the frequency of that local oscillator is dismm the frequency of the desired station. Thus it is sometimes necessar to readjust the local oscillator, whereby t is beat frepuency can no longer occur from the inerlng station. With theaid of my invention, this disadvanta e isovercome, and it is possible'to adjust t e frequency of the oscillator to its desired value once and for all the interfering signals are suppressed.

It is still another object. of my invention to improve in general, radio receivers in which electronic emission amplifiers or detectors are used.

My'invention possesses many other advantages, and has other objects which may be made more easily a parent from a consideration of several em odiments of my invention. For this purpose I have shown a few forms in the drawings accompanying and forming part of-the present specification. I i shall nowgproceed to describe these forms in detail, WhICh illustrate the general. principles 'ofmy invention; but it is to be understood that: this detailed description is not to be taken ina limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawings: Figure 1 is a wiring diagram of one form. of my. invention;

Fig. 2 is a graph illustrating the selectivity that may be expected with the aid of my in vention; and

Fig. 3 is a form of my invention embodied in connection with a ,superh-eterodyne receiver.

In Fig.1, I show an open pick-up circuit, including the elevated conductors 11, a loading inductance 12, a variable condenser 13, a variable resistor 14 and-the ground connection 15. By the aid of the variable condenser 13, this pick-up system can be tuned to the frequency at which reception is desired. The

variable resistance 14 is preferably tapered as indicated, to a maximum value of about 400 ohms. The drop across the resistance is the useful signalling volta received by the pick-up s stem. It is evi cut that interfermg signa s, which are not in tune with the pick-up system, do not cause as largea resistance drop in resistance 14 as the desired signals. Furthermore, by varying the resistance 14, the amount of energy by-passed thereb can be regulated, whereby a volume contro is secured.

In order to amplify the received signals, use can be made of any desired form of amplifiers or series of amplifiers. In the present instance, I indicate an electronic emission device 16 that is utilized as an amlifier for this purpose. However, any num- Ber of such devices can be used in cascade. It includes an evacuated vessel having therein an electron emitting electrode 17, such as a filament-adapted to be heated b the passage of an electric current; and a p ate electrode or anode 18 which receives the electrons emitted from electrode 17. This late electrode can be maintained ata positive potential with respect to the filament 17 as by aid of a battery 19, which is connected in an external circuit between these two electrodes. The space current between the filament 17 and the anode 18 is controlled by the control electrode 20, usually in the form of a grid interposed between the filament 17 and the anode 18. It has been found that even minute variations in potential difference between the electrodes 17 and 20 will cause correspondingly great variations in the electron flow from the filament 17 to anode 18. It is this effect which is utilized for amplification.

The input electrodes 17 and 20 of amplifier 16 are arranged to be affected by the potential difierences existing across the resistance 14, whereby the current flowing in the external circuit connecting the electrodes 17 and 1188 can be varied in accordance with these 51 a is output current can be passed through succeeding stages of amplifiers and detectors indicated by the rectangle 21, and finally to a translating device, 22, such as phones or a loudspeaker.

My invention relates more particularly to the manner in which the signalling potential difierences are impressed between the electrodes 17 and 20. First of all, there is a tunable series circuit, comprising for examle an inductance 23 and the variable conenser 24. One terminal of this circuit connects to the upper end N of the resistance 14. The point N at the other end of this series tuned circuit is therefore substantially of the same potential as the point N for electrical energy of the frequency that is in tune with the tuned circuit 23-24. In other extent of departure from resonance fre-- quency.

From point N to ground 15 there is another series tunable circuit, includin the series circuit formed by a variable con enser 25 and an inductance coil 26. The ground 15 is therefore another nodal point. Across this latter inductance coil 26 are connected the two input electrodes 17 and 20, whereby the potential differences across the inductance coil, are effective to control the space current in amplifier 15. This potential difference is a maximum for the frequency to which circuit 25--26 is tuned and is less for all other frequencies.

{1 resistance 27 can be connected between point N and ground 15. Since this resistance is connected across the series tuned circuit 2526, it is evident that it connects between two nodal points, and therefore there will be only a small drop across this resistance for the frequency of reception. However, for all other frequencies, some of the ener will be by-passed through this resistance Iaralleling the resistance 27 are two tuned series circuits, comprising respectively inductance 28 and variable condenser 29; and inductance 30 and; variable condenser 31. These tunable circuits are tuned respectively to a frequenc a little higher and a little lower than the requency at which reception is desired. For example, circuit 28-29 can be tuned to a frequency about ten or twenty kilocycles below the desired frequency of reception; while circuit 3031 may be tuned to a frequency ten or twenty kilocycles above the desired frequency of reception.

The result is that in connection with the band of frequencies having as limits the resonant frequency of the two tuned circuits 2829 and 3031, these circuits shunt interfering signals which are outside of that band. For example, if it be desired to receive signals carried on waves of 1,000 kilocycles, circuit 28--29 should be tuned to a fre uency of about 980 kilocycles, while circuit 3031 should be tuned to a frequency of about 1020 kilocycles. With such tuning, the response of the receiver is a maximum for the desired frequency, and it is a minimum at the frequency of resonance of circuits 28-29 and 3031.

This is graphically indicated in Fig. 2, wherein the line 32 represents the actual resonance conditions, secured by the system of Fig. 1; and the dotted line 33 represents a so-called ideal, which the system approaches. It is seen that the peak of curve 32 representing the desired carrier frequency, and

the narrow band adjacent to it afiect the receiver most stron ly. However interferin signals fall consi erably below the peak an therefore their audibility is lessened. It is thus seen that the effect of the use of the two tuned circuits is tocompres the actual curve of resonance 32, and thereby to sharpen the tuning.

border to make this system operate most effectively. It is of course desirable to keep the circuits 28-29 and 30-31 tuned tothe proper fre uencies for any frequency of reception. T is can be accomplished by a single dial tuning mechanism, in which condensers 13, 24, 25, 29, and 31 are simultaneously tuned so as to keep their respective circuits tuned to the pro r relative frequencies. ThlS can readily accomplished for example by the aid of mechanism disclosed in my prior Patent 1,707,948, granted April 2, 1929, and entitled Tuning system. Furthermore, in

order to ensure against any stray effects, the b tuned circuits can be encompassed in grounded metal shields. For example, circuit 23-24 can be closed in a grounded shield 34 and circuits 28-29 and 30-31 can be tively shielded by grounded shields 35 an 36; finally the amplifier16 with its assoc ated circuits can likewise be shielded, as indicated by the dotted line 37.

vThe fact that all the tuning elements of the system can be readily controlled by a single actuating member is of considerable importance, for by its aid, the proper relationship 3031 and the remaining circuits can always be maintained, without the necessity of tedious manipulation. This feature of umt control, I indicate by aseries of dotted lines 38 converging to a common polnt from the various tuning devices, and leadlng to the is end, Unit control.

he principle of by-passingparticularly annoying interfering oscillations is especially adaptable in connection with superheterodyne reception. Such a scheme is shown for example in Fig. 3.

In this case, a loop-pick-up circuit 1s illustrated, including the loop or coil 38}, and a tuning condenser 39 placed in series with the coil 38. The other side of the loop can be grounded as illustrated at 40. ThlS malice point 41 a nodal point, and from that point to ground 40, there is another tuned circuit including the variable condenser 42 and the coil 43. The circuit 38 -39 as well as the C11- cuit 42-43 should both be tuned to the desired frequency of reception. Furthermore, a. tapered variable resistance 44 can be connected across the tuned circuit 38 --39 to provide a volume control. A p

The electronic emission amplifier 45 has its input electrodes connected across the coil 43.

A battery or other source of potential 46 is utilized to provide a. negative bias on the between the circuits 2829 and grid electrode 47; and the ,output circuit includes. the plate or anode 48, the coupling.

coil 49and the plate battery 50. The amplified impulses present in coil 49 are transferred to a tunable circuit, includin thesecondary coil 51 and the variable con enser 52. This tunable circuit affects the first detector tube A 53. A local oscillator system 54 also affects theinput of the tube 53 in order to change the carrier frequency from that of the station from which the signals are received, to an intermediate value. This system 54 is shown in the present instance as comprising that condenser and coil 57. This latter coil also serves as a means for transferring the oscillations to the input side of the device 53, v

y being inductively coupled tothe coil. 58 located in the connection to the grid electrode of device 53. Device 53 can be arranged to act as a detector by means of a:

suitable grid bias battery 59. The output circuit of the first detector 53 that connects the anode 60 to the electron emitting filament 61, includes the primary coil 62 and a plate battery 63; In this external circuit ows a current that has a frequency equal to the beat frequency produced by the action of oscillator 54 upon the received oscillations in the pick-up circuit. This beat frequency is intermediate in value between the carrier frequency received,:and the audio frequency modulations thereof. f

As thus far described, this systeinis quite similarto that of an ordinary super-heterodyne system. The intermediate frequency waves are passed to an intermediate'frequency amplifier 64 coupled to the'output of;

the fiI'StdEtGCtOl 53. This amplifier can'com prise one or more stages of electronic emis sion amplifiers, all permanently tuned to a definite predetermined intermediate frequency, which can always be secured by proper manipulation of the oscillator system 54.

From the intermediate frequency amplifier 64, the amplified intermediate frequency energy can be passed to a second detector and audio frequency amplifier 65. From there the amplified audio frequency signaling currents can be passed to a translating device, such as a loudspeaker or phones 66.

Now let us assume that it is desired to receive from a station which is transmitting on 1,000 kilocycles. In-this case, circuit 38 39, 42-43, and 51-52 should be all accurately tuned to that frequency. The oscillator 54 can be tuned to a frequency either above or below.1,000 kilocycles to give a beat frequency of say 47.5 kilocycles. For this purpose it can be tuned for example to 952.5 kilocycles. This gives an intermediate frequency of 47.5

' is an interfering station sending strong signals at a frequency of 905 kilocycles. This may t through the tuned circuits referred to, with suflicient strength to produce a beat f uency with the fr uency of oscillator 54 o f the same value as be f cycles. In the past, in order to avoid such an interference, the frequency of the oscillator 54 was increased above 1,000 kilocycles so as to produce 1047.5 kilocycles, still iving the same beat frequency of 47.5 kilocyc es. In this way the .905 kilocycle station could be shut out. But such a shift in frequency of the oscillations produced by the oscillating system 54 may have the effect of makin it easy for another station to interfere. or

example, if there should be a station sending strong signals nearby, or at a short distance, on 1095 kilocycles, this would combine with the frequency of the oscillator 54 to give the same beat frequencyof 47 .5 kilocycles in the intermediate frequency ampli I overcome this interfering effect by the addition of a circuit between nodal point 41 and round 40, which comprises a tunable circuit having a variable condenser 66 and an inductance coil 67. This circuit is tuned to the frequency of the interfering signals and offers an effective b -pass for the interference without apprecia ly reducing the signals to be received. For example, the oscillator 54 can be set so as to be always 47 .5 kilocycles (or any intermediate frequency desired) below the frequency of the station from which signals are to be received. In that case, then circuit 66 67 must be correspondingly tuned kilocycles below the frequency to be received, since the only interfering station that could get through to affect the system would be a station sending out waves of a frequency of 95 kilocycles below the frequency of the station from which signals are to be received. This interfering ener y, however, will be by-passed throu h t e circuit 66 -67, and will not affect t e amplifier 45, nor the intermediate frequency-amplifiers 64.

As in the case illustrated in Fig. 1, all of the variable condensers or other variable tuning devices can be operated from a common control. This is indicated by the dotted line 68, leading to the legend Unit control. In order to increase selectivity and to ensure against stray affects, the circuits can also be shielded by grounded shields, such as indicated by dotted rectangles 69, 70, and 71.

ore; that is, 47.5 kilo=.

. I claim:

1. In a superheterodyne system of radio rece tion, in which there is a local oscillator the requency of which is adjustable whereby.

a beat frequency of a set constant value is secured for any frequency of reception, a tunable pick-up circuit including a resistor in series therewith, an electromc emission amplifier device having input electrodes and a tunable circuit having an inductance connected with said electrodes, said last named circuit being connected across said resistor, a second tunable circuit connected in parallel with said last named tunable circuit for bypassing energy from said pick-upcircuit, and a common control means arranged for simultaneousl tuning the pick-up circuit, for va ing the requency of the oscillator to provi e said constant beat frequency, and for tunin the energy by-pass circuit to a' value suc that it is resonant at all times to a frequency other than the signal frequency which is capable of producing the same constant beat frequency.

2. In a radio receiving system, the combination of a pick-up circuit includin a series connected inductance, variable con enser and variable resistor, means for applying signal potentials to said pick-up circuit, a second inductance, a second variable condenser and a second resistor connected in series across said variable resistor, a third variable con-.

denser, and a third inductance connected in series across said second resistor, a signal amplifier including an electronic emission device having input electrodes connected with said last named inductance and havin an output circuit, said circuits being tunabfia by means of said variable condensers to establish nodal points of potential at one terminal of each of said resistors.

3. In a radio receiving system, the combination of pick-up circuit including an inductance, a variable condenser and a variable resistor connected in series, means for applying signal potentials to said ick-up circuit, a second inductance, a second variable condenser and a second resistor connected in series across said variable resistor, a third variable condenser and a third inductance connected in series across said second resistor, an electronic emission device having input electrodes connected with said last named inductance and having an output circuit, said circuits being tunable by means of said variable condensers to establish nodal points of potential at one terminal of each of said resistors, and a pair of series resonant devices connected in parallel with said second named resistor, each of said devices being adapted to be tuned to a frequency differing from the frequency to which said pick-up circuit is tuned.

4. In a radio receiving system, the combination of a pick-up circuit including an inductance, a variable condenser and a resistor connected in series, a pair of tunable series circuits connected in parallel with said resistor, each of said tunable series circuits including an inductance, and an electronic emission device having input electrodes connected with one of said inductances and having an output circuit.

5. In a radio receiving system, the combination of an input circuit tunable for the reception of signal waves through a predetermined band of signal frequencies, said input circuit having a plurality of potential nodal points for the frequency of reception, two of said nodal points being in the high potential side and a third nodal point being in the low potential side of said input circuit, atunable series circuit connected between said first two nodal points, a second series tunable circuit connected between one of said nodal points and said third nodal point in the low potential side of the. input circuit, said last named tunable circuit including a reactanc e tuning device, an electronic emis- 2 sion device having input terminals connected across said reactance tuning device, and a signal output circuit for said electronic emission device.

In testimony whereof I have hereunto set my hand.

HAROLD F. ELLIOTT. 

